Brain Mechanisms

Androgens and aggression. I would like to make two comments regarding Dr Adams's thoughtful paper. The first is technical in nature and involves the statement that maternal aggression is enhanced by prolactin. Although this may be true for the hamster (see Wise and Pryor 1977), it is not the case for the rat and mouse. With regard to the former, Erskine, Barfield, and Goldman (1979) report the presence of postpartum aggression in the hypophysectomized rat. In addition, postpartum aggression remains intact in female mice administered ergocornine hydrogen maleate, a compound that blocks the release of prolactin from the pituitary (Gandelman, unpublished data). Thus, Adams's comment that "The effect of the prolactin upon defense is probably due to the suppression of the hypothetical 'consociate modulator and release of defense from its inhibitory Influence" must be clarified.

My second comment concerns Adams's discussion of fhe motivating stimuli for offense. It was correctly pointed out that in many muroid rodents one of the principal stimuli for the initiation of aggressive behavior is olfactory in nature, is testosterone-dependent, and is effective primarily in males. Moreover, it was speculated that the "sensory filters" or CNS receptor mechanisms for these stimuli are dependent upon testosterone.

The notion that testosterone is involved in both the emission of the cue and its reception is an important one, In that it may shed light upon the manner in which androgen initiates or activates fighting behavior. The study of aggressive behavior in rodents has taken two ostensibly divergent paths. European investigators, for the most part, have been concerned primarily with specifying the stimuli that elicit fighting behavior. Some of the major findings have been that males emit an odor found in the urine that elicits aggression from other males, and that this olfactory cue or releaser pheromone is androgen-dependent, being absent in castrate male mice and females and present following the administration of testosterone (Mugford and Nowell 1970a; 1970b; 1971). If has also been reported that ablation of the olfactory bulbs, as well as masking of natural odors by adulterating mice with odorants reduced fighting behavior (Ropartz 1968).

In the US many investigators have been interested in the hormonal involvement in aggression and in the influence of androgen in particular. The finding that castration abolishes aggression in male mice. and that testosterone replacement is restorative (Beeman 1947), was followed nearly twenty years later by reports demonstrating that the administration of testosterone to females can cause them fo fight (Edwards 1968, Bronson and Desjardins 1970; Svare, Davis, and Gandelman 1974).

Summarizing the two principal paths taken by researchers interested In aggressive behavior, we have those who have shown that an androgen-dependent olfactory stimulus plays an important role in triggering fighting behavior, and others who have reported that testosterone is responsible for establishing the propensity of an animal to fight. One of the major questions posed by behavioral endocrinologists concerns the manner in which hormones affect behavior The data cursorily summarized above suggest that androgen affects the CNS in such a way as to render it uniquely responsive to the aggression- promoting olfactory stimulus emitted by the opponent. In other words, in the absence of relatively high levels of androgen, the olfactory stimulus is either not "perceived," or it lacks certain "information value." It is unlikely that animals devoid of gonadal androgen fail to detect the olfactory stimulus. It is more likely that this olfactory cue possesses little if any information relevant to the status of the other animal (the potential opponent) in the absence of testosterone at a level normally found in the male. In the parlance of Adams, the sensory filters would not be activated in the absence of testosterone. However, it would appear that the term "sensory filter" should be replaced by "sensory analyzer."